Based on the hypothesis that teachers possessing extensive and coherent knowledge structures are the most effective teachers, this paper explores the use of a modified ordered tree (OT) technique for measuring teachers' knowledge structures. Two questions are posed: (1) Can a modified OT technique be used to measure teachers' knowledge structures? and (2) Is there a relationship between teachers' knowledge structure scores and their ability to be adaptive during instruction? Using 8 experts, 16 novices, and 4 uninstructed learners, 3 studies were conducted. Results indicate that the modified OT technique describes longitudinal changes in novice teachers' knowledge structures during reading methods course instruction, and that novices' knowledge structures are associated with adaptive instructional actions. Implications for teaching and teacher education are suggested. (Author)